The hypothesis to be tested in this study is that prospective investigation of families with MEN I will allow early detection, syndrome delineation, and improved outcome. MEN-I is an autosomal dominant inherited disorder of dysplasia of the anterior pituitary gland, the islet cell of the pancreas and the parathyroid glands. Patients with the syndrome have a diverse spectrum of initial presentation which has led to significant understanding of the disorder. Although MEN-I is expressed with high penetrance, at diagnosis most patients have symptoms of only one endocrinopathy or are asymptomatic. This study, therefore, screens family members of patients for a variety of endocrinopathies.